US9939506B2ActiveUtilityPatentIndex 71
Methods of investigating formation samples using NMR data
Est. expiryJun 8, 2032(~5.9 yrs left)· nominal 20-yr term from priority
Inventors:VENKATARAMANAN LALITHAGRUBER FRED KHABASHY TAREK MAKKURT RIDVANVISSAPRAGADA BADARINADHLEWIS RICHARD ERYLANDER ERIK
G01R 33/448G01V 3/38G01R 33/54G01V 3/32G01N 24/081G01V 3/14G01N 24/08
71
PatentIndex Score
3
Cited by
34
References
10
Claims
Abstract
A methods are provided for investigating a sample containing hydrocarbons by subjecting the sample to a nuclear magnetic resonance (NMR) sequence using NMR equipment, using the NMR equipment to detect signals from the sample in response to the NMR sequence, analyzing the signals to extract a distribution of relaxation times (or diffusions), and computing a value for a parameter of the sample as a function of at least one of the relaxation times (or diffusions), wherein the computing utilizes a correction factor that modifies the value for the parameter as a function of relaxation time for at least short relaxation times (or as a function of diffusion for at least large diffusion coefficients).
Claims
exact text as granted — not AI-modifiedWhat is claimed is:
1. A method of investigating a geological formation traversed by a borehole, comprising:
a) obtaining a nuclear magnetic resonance (NMR) tool;
b) subjecting a sample of known porosity to a nuclear magnetic resonance (NMR) sequence with a pulse echo spacing using the NMR tool;
c) determining a normalized bias B(T 2 ) of said NMR tool as a function of T 2 relaxation times;
d) locating the NMR tool in the borehole and detecting signals in response to said NMR sequence at at least one depth in the borehole;
e) analyzing a decay of the detected signals with a computer processor, in order to extract a distribution of the T 2 relaxation times; and
f) computing and providing, with the computer processor, a value for porosity of the formation at said depth as a function of at least one of said T 2 relaxation times, wherein said computing utilizes a correction factor that modifies the value of the parameter as a function of the T 2 relaxation time for at least the T 2 relaxation times occurring on the order of said pulse echo spacing, wherein said correction factor is a function of said normalized bias.
2. A method according to claim 1 , wherein:
said pulse echo spacing is approximately 0.2 ms, and
said relaxation times on the order of said pulse echo spacing are 1 ms and less.
3. A method according to claim 1 , wherein:
said correction factor is c f (T 2 )=1/(1+B(T 2 )).
4. A method according to claim 2 , wherein:
B
(
T
2
)
≈
ϕ
^
(
T
2
)
-
ϕ
T
ϕ
T
where ϕ T and {circumflex over (ϕ)}(T 2 ) are respectively a true and an estimated porosity of a calibration sample obtained from a porosity sensitivity curve for said NMR tool.
5. A method according to claim 1 , wherein:
said correction factor is
c
f
(
T
2
)
=
1
1
+
B
(
T
2
)
R
(
T
2
)
β
(
R
(
T
2
)
)
+
R
(
T
2
)
where
R
(
T
2
)
=
ϕ
^
(
T
2
)
σ
ϕ
(
T
2
)
and corresponds to a signal to noise ratio for a given T 2 , β is a scalar, < > is an average computed over T 2 ,
B
(
T
2
)
≈
ϕ
^
(
T
2
)
-
ϕ
T
ϕ
T
is the relative bias obtained from an NMR sensitivity curve of said NMR tool where ϕ T is a true porosity of a calibration sample and ϕ(T 2 ) is an estimated porosity of the calibration sample, and σ ϕ is a standard deviation of the estimated porosity.
6. A method according to claim 5 , wherein:
said correction factor tends to a value of 1 with respect to a particular T 2 relaxation time when said signal to noise ratio is small for that particular T 2 relaxation time.
7. A method according to claim 1 , further comprising:
using said value of porosity obtained utilizing said correction factor in order to obtain determinations of at least one additional parameter of said sample at said depth.
8. A method according to claim 7 , wherein: said at least one additional parameter of said sample is one of rock permeability, hydrocarbon viscosity, bound fluid volume, and free fluid volumes.
9. A method according to claim 7 , wherein: said at least one additional parameter of said sample is organic content of said sample.
10. A method according to claim 7 , wherein: said at least one additional parameter of said sample is montmorillinite content.Cited by (0)
No later patents cite this yet.
References (0)
No backward citations on record.